UPDATE 3/30: We have released Windows 10 Insider Preview Build 17133 (RS4) to Windows Insiders in the Slow ring. As part of this flight, we are testing the engineering systems responsible for the deployment of Windows 10 feature updates to customers. As such, not all Insiders in the Slow ring will be immediately targeted to receive this flight. We are targeting full availability to the Slow rinf on Monday 4/2 t however, if you’d like to install immediately, a manual check for updates under Settings > Update & Security > Windows Update will present the build.